In recent years, a greater emphasis has been placed on the use of insulation materials in dwellings or other structures to promote energy conservation and noise reduction. At the same time, innovative architectural designs have created a variety of shapes and sizes that do not always lend themselves to the use of a conventional fibrous batting, which is often available in rolls of uniform width. This has created a need for a technique for applying fibrous insulation that does not use uniform width batting.
This need has been fulfilled to a limited extent by developing various blown-in-place insulation techniques, wherein loose-fill fibrous insulation is blown into a cavity between the framing members of the wall, ceiling, or floor of a dwelling. The loose-fill insulation is provides a low cost installation techniques and is perceived as capable of completely filling the cavity, regardless of its shape and size, achieving a uniform volume of insulation for optimum energy conservation, as well as sound insulation purposes.
While blown-in-place insulation techniques provide a low cost method of installing insulation, one of the advantages of batting lost to blown-in-place insulation is the batting's ability to provide a predetermined insulation value, also known as the “R-value”. The R-value can be determined by the thickness (T) of the fibrous insulation and the insulation constant (k) using equation 1.R=T/k  (1)
In the manufacture of fiberglass batts it is a relatively simple matter to determine the nominal thickness and insulation constant to determine the R-value of the batt. This R-value is then printed on the batt during manufacture. When insulation batting is purchased, for example, to place in a new dwelling, it is often purchased by specifying a desired R-value. If installed in accordance with minimal prescribed installing techniques, the purchaser, due to uniform dimensions of insulation batting, can be count on at the insulation value having a certain thermal resistance.
The R-value of blown-in-place insulation is determined by Eq. 1 (above), however k is dependent on the density of the insulation. Therefore, one advantage of the easily determined R-value associated with batting is typically not applicable. As a consequence, it is necessary to also employ a secondary technique for determining the density of the blown-in-place insulation for assuring that the insulation has the desired R-value.
Various secondary techniques have been employed for the determining density in blown-in-place fibrous insulations. In one technique, a known mass of loose-fill is blown into a cavity of a known volume. The mass is divided by the cavity volume to determine density and R-value. A problem with this technique is that it slows down the installation process of the insulation and therefore, may not be easily used in the field. It is also difficult to calculate the actual volume of the cavity because there are typically features such as windows, doors, devices in the area that take up volume. Further, inexperienced insulation installers may not provide an even volume filling density that causes the density and R-value to vary between cavities.
In another known technique, a space is first filled with blown-in-place insulation. Then, a sample of insulation of a known volume is removed from a wall cavity and weighed. Using the volume of the sample, it is possible to determine the density of the insulation in the cavity by weighing the sample and dividing the weight by the known volume. The R-value of the insulation may then be determined in a known manner simply by knowing the thickness of the insulation in the cavity. In some instances, the quantity of insulation may be loose or compressed. As a consequence, error in determining the density of the insulation can be magnified if care is not taken to correctly remove the sample or average a number of samples. This is also a very time consuming technique and consequently is not preferred by insulation installers.
In yet another known technique, netting is secured to wall studs to.enclose an underlying cavity. Insulation is blown into the cavity through a hole in the netting. The netting retains the insulation in the cavity. U.S. Pat. No. 4,712,347 to Henry V. Sperber discloses observing the bulging out of the netting as a signal that a sufficient amount of insulation has been fed into the cavity behind the netting. This technique is unreliable because it is based on the subjective observation of the insulation installers and the tension of the netting applied to the cavities. Moreover, the mechanical properties such as the modulus of elasticity of the netting material affect the resiliency of the netting and the appearance of the bulge. In addition, the modulus of elasticity of the insulation, which is affected by the fiber diameter and the presence or absence of a binder, controls the resiliency of the insulation. Environmental conditions, such as humidity, may also affect the accuracy of the technique. Another disadvantage of this technique is that installers, in an effort to insure that a cavity is adequately filled, often overfill the cavity. Overfilling the cavity is undesirable because it causes the netting to bulge too much and wastes insulation. If the netting bulges too much, wallboard is difficult to install on the framing members. This has been recognized as a problem and thus has led to the use of a shield during installation, whereby the shield is held against the netting while the cavity is being filled to prevent the netting from bulging undesirably.
In view of the above techniques, it is apparent that there exists a need in the art for an improved apparatus and method for installing insulation that is blown into open wall cavities to a prescribed density wherein the improved apparatus and method provide increased accuracy.